v4.19.13 snapshot.
diff --git a/arch/x86/kernel/apic/x2apic.h b/arch/x86/kernel/apic/x2apic.h
new file mode 100644
index 0000000..a49b360
--- /dev/null
+++ b/arch/x86/kernel/apic/x2apic.h
@@ -0,0 +1,9 @@
+/* Common bits for X2APIC cluster/physical modes. */
+
+int x2apic_apic_id_valid(u32 apicid);
+int x2apic_apic_id_registered(void);
+void __x2apic_send_IPI_dest(unsigned int apicid, int vector, unsigned int dest);
+unsigned int x2apic_get_apic_id(unsigned long id);
+u32 x2apic_set_apic_id(unsigned int id);
+int x2apic_phys_pkg_id(int initial_apicid, int index_msb);
+void x2apic_send_IPI_self(int vector);